Deep-sea skates, relatives of sharks and rays, were discovered laying their eggs adjacent to hot water from hydrothermal vents. Scientists think that the marine animals use the heat to speed up the development of their embryos.

Accidental Discovery Of Deep-Sea Skate Nurseries Around Hydrothermal Vents

Brennan Phillips, from the University of Rhode Island, and colleagues were exploring the seafloor of the Galapagos Island in 2015 when they found large numbers of egg cases of the deep-sea skate.

After analyzing the water temperatures and the locations of the eggs, the researchers realized that these littered in hot water around known locations of hydrothermal vents, an opening in the sea floor out of which geothermally heated water flows.

"Hydrothermal vents are the result of seawater percolating down through fissures in the ocean crust in the vicinity of spreading centers or subduction zones (places on Earth where two tectonic plates move away or towards one another). The cold seawater is heated by hot magma and reemerges to form the vents," the National Ocean Service explains.

Phillips and colleagues concluded that the eggs were intentionally placed in locations where the water was warmer.

Just The Right Temperature

The eggs were not right next to the active vents because the temperatures there could get so hot and kill the embryos. Most of the eggs were found in lukewarm water not far from the vents but near some extinct vents.

Of the 150 egg pouches that the researchers observed, 58 percent were found within 20 meters of a black smoker, the hottest kind of vent.

Eighty-nine percent of the eggs cases were laid in water that was hotter compared with the background temperature.

Incubating Eggs Underwater

Deep-sea skates have some of the longest known egg incubation times. The researchers believe that the skates strategically placed their eggs in these warm locations to accelerate the development of their embryos.

"We report for the first time, a unique behavior where the deep-sea skate, Bathyraja spinosissima, appears to be actively using the elevated temperature of a hydrothermal vent environment to naturally 'incubate' developing egg-cases," the researchers wrote in the journal Scientific Reports on Feb. 8.

Egg Cases Of Rays And Sharks Also Seen Near Hydrothermal Vents

Interestingly, shark experts also reported seeing egg cases of sharks and rays near hydrothermal vents.

"[W]e showed our data to a bunch of shark experts, and they had seen anecdotal evidence of shark and ray egg cases near hydrothermal vents," Phillips said.